As is known in the art, the processing of wafers is facilitated if the wafer is clamped substantially flat against a support base or backplate which is temperature controlled during wafer treatment. By clamping the wafer, the number of points of contact between the wafer and the support is increased whereby the thermal conductivity between the wafer and the support is increased and wafer warps are corrected. The improved heat transfer to or from the wafer enables better control of the temperature of the wafer and, hence, better process control. These considerations are discussed, for example, in U.S. Pat. No. 5,055,964, issued on Oct. 8, 1991 to Joseph S. Logan et al, and assigned to the present assignee.
The cited patent further sets forth that in both known types of electrostatic chucks (single area or split area electrode), an electrode is positioned on a support base. An insulator is placed over the electrode and, in turn, the wafer is placed over the insulator. Voltage is applied between the single area electrode and the wafer or between the split areas of the electrodes, as the case may be, creating an electrostatic force of attraction. The amount of electrostatic attraction between energized chuck and wafer depends upon a number of factors, among which is the thickness of the insulator. In order to determine accurately the magnitude of electrostatic attraction, it is necessary that the insulator thickness be formed with close precision, the force of attraction being very sensitive to small thickness deviations.